Dry silver recording paper is used in a number of analytical and recording instruments which, in general, include an arrangement for developing the recording paper as it leaves the apparatus. Dry silver recording material is developed by heat. Conventionally, the exposed paper is passed over a heated platen. The development process must be controlled within certain limits, since if the recording material is overheated due either to excess temperature or inadequate transport speed, discoloration of the recording results while if the material is underheated, contrast in the developed image is reduced. It is therefore necessary to adjust the development conditions if the rate of transport of the recording paper through the recording equipment is to be varied. This normally involves either changing the length of platen over which the recording paper moves, or changing the temperature of the platen.
Particular problems are involved if the recording paper is transported at a very slow speed. Since a minimum temperature must be achieved in order to provide satisfactory development, only a short platen can be used. The present invention aims to provide a development unit for developing dry silver recording paper which unit can be used over a relatively wide range of paper speeds including very slow speeds.